Ptolemy's 12th star of Hydra (α Hydræ) is, Al-Sufi says, "the bright red star which is found at the end of the neck where the back begins; it is of the 2nd magnitude. It is that which is marked on the astrolabe as _unk al-schudja_, 'the neck of the serpent,' also _al-fard_, 'the solitary one.'" Al-Sufi's estimate of its brightness agrees well with modern measures; but it has been suspected of variable light. Sir John Herschel's estimates at the Cape of Good Hope varied from 1·75 to 2·58 magnitude. He thought that its apparent variation might be due to its reddish colour, and compares it to the case of α Cassiopeiæ. But as this latter star is now _known_ to be irregularly variable it seems probable that α Hydræ may be variable also. Gemmill found it remarkably bright on May 9, 1883, when he thought it nearly equal to Pollux (1·2 magnitude). On the other hand, Franks thought it nearer the 3rd than the 2nd magnitude on March 2, 1878. On April 9, 1884, the present writer found it only slightly less than Regulus (1·3 magnitude). On April 6, 1886, how-ever, it was considerably less than Regulus, but half a magnitude brighter than β Canis Minoris, or about 2½ magnitude. In the Chinese Annals it is called the "Red Bird." In a list of thirty stars found on a tablet at Birs-Nimroud, it is called "The son of the supreme temple." Although to the naked eye deserving the name of Alphard or "the solitary one," it is by no means an isolated star when examined with a telescope. It has a faint and distant companion, observed by Admiral Smyth; and about 25' to the west of it Ward saw a small double star (8, 13: 90°: 50"). With a 3-inch refractor in the Punjab, I saw a small star of about 8½ magnitude to the south and a little east of the bright star, probably identical with Smyth's companion. Farther off in the same direction I saw a fainter star, and others at greater distances in the field. There is also a faint star a little to the north. I also saw Ward's double with the 3-inch telescope. There is some difficulty in identifying the stars numbered by Ptolemy 13, 14, and 15 in Hydra. Having plotted a map from Ptolemy's positions (as given by Al-Sufi), I have come to the conclusion that Ptolemy's stars are 13 = κ Hydræ; 14 = υ; and 15 = λ Hydræ, probably. From the clear description given by Al-Sufi of the stars observed by _him_, I find that _his_ stars are 13 = υ_{1}; 14 = υ_{2}; and 15 = λ Hydræ. We must, therefore, conclude that Ptolemy and Al-Sufi saw only three stars where now there are four,[443] and that κ Hydræ was not seen, or at least is not mentioned by Al-Sufi. κ is, therefore, probably variable. It was rated 4 by Tycho Brahé, Bayer, and Hevelius; it is at present about 5th magnitude. If Ptolemy did not see υ_{2} it is probably variable also, and, indeed, it has been suspected of variable light.[444]